Suspended Structures

Alamillo Bridge by Calatrava | Suspended Structures

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Alamillo Bridge, Seville, Spain | Suspended Structures

In my previous article, we discussed the development of Suspended Structures and the technical aspects involved in the construction of Suspended Structures.

Alamillo Bridge, Seville, Spain, 1987-1992, designed by Calatrava Santiago, total span of the bridge is 250m and height of the tower is 142m. Materials used are steel for tower with concrete infill where needed, steel bridge deck structure and concrete abutments. The extraordinary weight of the concrete filled steel mast, which angles away from the roadbed at 58 degrees is enough to support the deck without the need for counter-stay cables or support piers.

Alamillo Bridge, Seville, Spain | Suspended Structures
Alamillo Bridge, Seville, Spain | Suspended Structures

The mass and the bed of the tower exerts a backwards downward force while the cable stays and roadbed mass exert a forward downward force. The mass of the tower was so calculated so that its backward and downward force wouldn’t lift the bridge off the ground.

For this reason, an additional mass was needed to counter the reaction of vertical forces. In order to increase the mass, the steel box girder of the tower and the steel deck structure were filled with concrete. This added to the stability of the structure.

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Development of Suspended Structures | Structural Systems

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Suspended Structures | Structural Systems

Suspended Structures are those with horizontal planes i.e. floors are supported by cables (hangers) hung from the parabolic sag of large, high-strength steel cables. The strength of a suspended structure is derived from the parabolic form of the sagging high strength cable.

To make this structure more efficient, the parabolic form is so designed that its shape closely follows the exact form of the moment diagrams.

The sagging cable is more stable under symmetrical loading conditions as the cable may deform as it attempts to adjust to an eccentric loading. As the cable adjusts to this load its shifts the rest of the structure.

 

Dulles International Airport
Dulles International Airport

 

This adjustment causes secondary stresses in the horizontal surface and additional deformation. The parabolic curve of the cable is also designed for various eccentric or lateral loads such as wind, seismic etc.

The large curving cable may consist of many smaller cables which are tightly spun together. As the cables are being spun together, they are also stretched over the span and attached to the supports.

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